Retarding diffusion of sensitizing dyes



May 15, 1945. c. J. STAUD 2,376,202

RET ARDI NG DIFFUSION 0F SENSITiZING DYES Filed May 27, 1943 BLUE-SENSITIVE EMULSION YELLOW FILTER GREEN-SENSITIVE EMULSION LIPPMAN TYPE EMULSION RED-SENSITIVE EMULSION SUPPORT cYRIL J. STAUD INVENTOR A TTORNE YS Plume May is, 1945 cyru J. Stand, Rochester, is. Y., minor to maman Kodak poration of New Jersey Application my 21, 1943, Serial No. aces 6 Claims.

This invention relates to color photography and particularly to a method for retarding or preventing the din'usion of optical sensitizing dyes.

In the usual type of multi-layer photographic ;material the separate silver halide emulsion layers are sensitized to the various spectralregions with optical sensitizing dyes. Such dyes'are believed to be adsorbed to the silver halide grains but this adsorption is not complete in every case and the dyes are not retained in the emulsion in which they are originally incorporated. When the sensitizing dye diflfuses from the layer in which it is incorporated and passes into an adjoining sensitive layer, it becomes adsorbed to the silver halide grains in that layer and thereby causes the adjoining layer to record light which it was not intended to record. The difiusion of the sensitizing dyes, therefore, destroys accurate color rendition by the multi-layer system. A great many optical sensitizing dyes are known which afl'ord i'airly satisfactory results as regards their sensitizing properties but which difi'use from ent invention to provide a method for reducing the tendency of optical sensitizing dyes to wander from one silver halide layer to another. A further object is-to provide a novel multi-layernma- Company, Rochester, N. Y., a. cordyes in either the red-sensitive emulsion or the green-sensitive emulsion may difluse intoadjacent emulsion layers and cause them .to record light which they were not intended to record. For example, the optical sensitizing dye in the redsensitive emulsion layer might difiuse into the green-sensitive emulsion layer or into thebluesensitive emulsion layer. The optical sensitizing dye in the green-sensitive emulsion layer may difi'use either into the red-sensitive emulsion layer or into the blue-sensitive emulsion layer. Optical sensitizing dyes which diffuse to any extent to adjacent layers cannot be used in practice since it is important that the sensitivity of the vario layers be well defined,

I have found that the introduction'of a very emulsion layers a multi-layer material is etiective in reducing the tendency of the optical sensitizing dyes to contaminate adjacent layers. The

I ,emulsion used in this interlayer is preferably a terial in which the color rendition is not degraded by the diffusion of the sensitizing'dye.

These objects are accomplished according-to my invention by coating a layer of a fine grain,

uniogged, slow-speed, silver halide emulsion adjacent a silver halide emulsion layer containing a sensitizing dye which difi'uses, or between the coated in superposed relationupon it. These emulsion layers are generally sensitized-with optical sensitizing dyes to various regions 01' the visihle spectrum. The customary three-layerimaterial has adjacent the support a red-sensitive emulsion and this is followed in order by. a greensensitive emulsion and an unsensitized emulsion which is blue-sensitive. The optical sensitizing fine-grain geiatino-silver halide emulsion of the modified Lippmann type, which is very satisfactory for preventing the optical sensitizer from reaching the next color-sensitive layer. While I do not postulate the mechanism of this action. it appears probable that the d-ifl'using dye is adsorbed to the very fine particles of the silver .layer material ordinarily has a yellow filter layer in or beneath the top blue-sensitive layer and the interlayer which I propose to use may contain the yellow filter dye. The modified Lippmann emulsions of the type which I propose to use are sumcientlyfine grained that they are quite transparent and, therefore, do not decrease the resolvingpower or definition of the image in'the under-;

lying layers. They absorb only blue and violet light, and being placed, according to my invention, below the yellow filter layer, they. do not reaching the adjoining color image readily removable during ordinary g of the material and, therefore, requires no extra step during processing for its removal.

The following specific examples will serve to illustrate my invention:

Ezampie 1 A moderate speed emulsion suitable for use in color photography was sensitized to red light with 1ZZ GiethyIthia-i-carbocyanine iodide in a concentration of 100 milligram of dye per 16,000 cc. of emulsion. ()ver this was coated in one instance a clear gelatin layer and in the other case a modified Inppmann type emulsion coated oi the same thickness as the gelatin layer. these layers was then coated ablue-sensitive emulsion similar to that used in the optically sensitized layer, but without the sensitizing dye.

When the resulting films were exposed from the front in a wedge spectrograph, developed and fixed, it was found that in the case where the plain gelatin interlayer was used a considerable amount of imagewas obtained in the top emulsion in the red-sensitive region, whereas in the coating containing the modified Lippmann type emulsion in the interlayer the image in the red region of the spectrum wasconflned to the first coated or lowermost emulsion layer. This clearly indicated that the interlayer of Lippmann type emulsion had prevented diflfusion of the optical sensitizing dye from the lower layer into the upper layer.

Example 2 slum bromide solution'containing 0.2% potassium iodide. These are added over a period oi approximately 5 minutes either continuously or intermittently. The temperature is maintained at 30 C. during this time. The material is then cooled, setting it to a mm gel, and shredded. It is washed briefly, in a manner well known in the art, to remove soluble salts and is again melted and is ready for coating. My invention 'will now be described by reference to the accompanying drawing.

As shown in the drawing, in is ,a support of any suitable material such as, cellulose nitrate,

cellulose acetate, paper, pigmented cellulose ester.

Above or synthetic. resinhaving thereon a red-sensitive emulsion layer II, a, Lippmann type emulsion interlayer i2, according to my invention, a greensensitive emulsion layer IS, a yellow filter layer M and a blue-sensitive emulsion layer I5. As

pointed out above, the layer M may also contain a fine grain'slow speed emulsion according to into. the layer IS. The emulsion layers ll, I2 and ii are the usual gelatino-silver halide emulsion layers customarily used in multi-layer photographic elements. These emulsions may also consist of. silver halide dispersed in other waterpermeable colloidal materials such as cellulose estersjor ethers or synthetic resins.- The emul sion layers II, is and i5 may also contain colorforming compounds as disclosed, ior example, in

-Mannes and Godowsky U. S. Patent 2,3il4fiilil,

granted December 15, 1942.

It will be understood that the examples and modifications included herein are illustrative only and that my invention is to be taken as limited only by he scope or the appended claims.

I claim:

graphic silver halide emulsion layer to the grains of another photographic silver halide emulsion layer coated in proximity to the first layer, at least one of said emulsion layers containing an optical sensitizing dye having a tendency to diffuse, which comprises incorporating as a layer between said silver halide emulsion layers, a layer of an unfogged silver-halide emulsion, said lastmentioned layer being sufllciently fine-grained that it is transparent and does not decrease the resolving power and definition of any underlying layer, and being sufilciently insensitive to light that it is not rendered developable in the usual length of time during which the film is exposed.

2. The method of retarding diffusion of optical sensitizing dyes from a photographic silver halide emulsion layer sensitized to a wave-length oflldht longer than blue with said sensitizing dyes, to another photographic silver halide emulsion layer sensitive to a different spectral region and coated in proximity to said first-mentioned emulsion layer, at least one of said layers being sensitized with a dye having a tendency to difiuse, which comprises incorporating as a layer between said emulsion layers, a layer of an unfogged. silver bromide emulsion, said last-mentioned layer being sufliciently fine-grained that it is transparent and does not decrease the resolving power and definition of any underlying layer, and being sufficiently insensitive to light that it is not rendered developable inthe usual length of time during which the film is exposed.'

3. The method of retarding diffusion or the optical sensitizing dye from a red-sensitive gelatino-silver halide emulsion layer sensitized with tion of any underlying layer, and being sufliciently insensitive to light that it is not rendered'developable in the usual length of time durin which the film is exposed.

4. A multi-layer photographic element in which the tendency of optical sensitizing dyes to diffuse intc adjacent sensitive layers is reduced, comprising a plurality of silver halide emulsion layers sensitized to different spectral regions, at least one of said emulsion layers containing an optical sensitizing" dye having a tendency to diffuse, and between said last menti'oned layer and another, differently-sensitive layer, a layerof an unfogged silver halide emulsion, said last-mentioned layer being sufliciently fine-grained that it is transparent and does not decrease the resolving power and definition of any underlying layer, and being sufficiently insensitive to light that it is not rendered developable in the usual length of time during which the film is exposed.

5. A multi-layer photographic element in which the tendency of optical sensitizing dyes to diffuse into adjacent sensitive layers is reduced, comprising at least two superposed gelatino-silver halide emulsion layers sensitive to different regions of the visible spectrum, at least one of which layers contains an optical sensitizing dye having a tendency to diffuse into said superposed layer, and between said layers. a layer of an unfogged silver bromide emulsion, said last-mentioned layer being sufiicientiy flneegrained that it is transparent and does not decrease the resolving power and definition of any underlying layer, and being sufficiently insensitive to light that it is not rendered developable in the usual length of time during which the film is exposed.

' 6. A multi-layer photographic element in which the tendency of optical sensitizing dyes to diffuse into adjacent sensitive layers is reduced and does not decrease the resolving power and definition of any underlying layer, and being sufficiently insensitive to light that it is not rendered developable in the usual length of time during which the film is exposed.

- CYRIL J. STAUD. 

